1387, "hard, unbreakable," from earlier noun (O.E.
aðamans) meaning "a very hard stone," from L.
adamantem (nom.
adamas), from Gk.
adamas (gen.
adamantos) "unbreakable," the name of a hypothetical hardest material, perhaps lit. "invincible," from
a- "not" +
daman "to conquer, to tame" (see
tame), or else a word of foreign origin altered to conform to Gk. Applied in antiquity to white sapphire, magnet, steel, emery stone, and especially diamond (see
diamond). Fig. sense of "unshakeable" first recorded 1677.
Adamantine (adj.) first recorded 1382.